Conventionally, it is necessary to authenticate whether, in Internet and the like, data inputted in a user terminal is inputted by an operation by a person or is automatically inputted by a program and the like (that is, inputted by the above bot). More specifically, when a review article about such as a product, hotel is written, a comment on a web log is written or various files are downloaded, it is necessary to authenticate whether or not these are executed based on operations by a person.
As an example of a technique for the above authentication, a so-called CAPTCHA technique is known. With this CAPTCHA technique, numbers or characters which have broken shapes or are made partially defective to allow only people to recognize are displayed on a display of a user terminal. Further, when a person who views these numbers and characters inputs, for example, characters the person views and the inputted characters match with characters which are displayed, it is authenticated that the person is actually inputting the characters. The citation list which discloses this CAPTCHA technique includes, for example, following Patent Document 1.